Diode pulse amplifier



May 7, 1957 Filed April 28, 1951v -c. R. WILLIAMS 2,791,725

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May 7, 1957 c. R. WILLIAMS 2,791,725

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DIODE PULSE AMPLIFIER 4 Sheets-Sheet 4 May 7, 1957 Filed April 28, 1951 THA/cs) nid States Patent F DIDEPULSE AMPLIFIER Charles R. Williams, Hawthorne, Calif., assignor to Nor-` throp Aircraft, Inc., Hawthorne, Calif., a corporation of California Application April 28, 1951, Serial No. 223,565

6 Claims. (Cl. 315-166) a large pulse source by employing suitable connected l capacitance.

It is an object of this invention to provide a simple and eifective gas-iilled diode pulse amplilier.

Briey, the foregoing object and -other objects ancillary thereto are preferably accomplished byproviding a subminiature diode glow tube containing two cold electrodes of ordinary wire and filled with an inert gas such as neon, for example, at glow discharge pressure. The tube is normally maintained conducting by a high electrode voltage supplied through a current hunting resistance. Input pulses, which are to be amplified in the output, are applied to the diode such that each causes momentary quenching of the glow discharge. Subsequent retiring of the diode forced by the high supply voltage causes an output pulse to be emitted after each input pulse. Following quenching of the glow discharge, energy storage occurs in capacitance in the output circuit, and the output pulse is derived from the sharp drop in tube potential upon retiring. The output pulse amplitude is directly a function of the diode characteristic, that is, the difference between its tiring and burning potentials, and is independent of the amplitude of the input pulse provided that the input pulse has suicient amplitude for quenching. The time delay between the input pulse and the output pulse, and the energy delivered by the output pulse are both directly a function of the storage capacitance associated with the output circuit. The tube can be made more sensitive to the input quenching pulses by the use of a small percentage of a polyatomic quenching gas or vapor mixed with the inert gas. Y

The invention possesses other objects and features, some of which, together with the foregoing, will be set forth in the following description of a preferred embodiment of the invention, and the invention will be more fully understood by reference to the accompanying drawings in which:

Figure 1 is a drawing showing a view of a preferred embodiment and construction of the diode glow tube.

Figure 2 is a drawing showing a circuit used whereby the voltage-current characteristics for the diode can be obtained.

Figure 3 is a graph of the electrical characteristics of the diode glow tube filled with an inert gas at glow discharge pressure.

Figure 4 is a graph of the deionizationcharacteristics A .2,791,725 Patented May 7, 1957` of the diode glow tube lled with an inert gas at glowY discharge pressure.

Figure 5 is a drawing showing a circuit in which the diode glow tube can be quenched and controlled by suitable input pulses.

Figure 6 is a graph of the triggering response of the diode glow tube for the circuit of Figure 5.

Figure 7 shows a block diagram of the diode amplifier.

Figure 8a is a drawing illustrating a circuit in which the diode glow tube isconnected as an oscillator.

Figure 8b is a drawing showing a circuit wherein the oscillator of Figure 8a can be resistively damped to prevent oscillation.

Figure 8c is a drawing of .another damping circuit wherein oscillation can be prevented in the oscillator of Figure 8a.

Figures 9a, 9b, 9c, 9d and 9e show various input circuits with negative pulse source and which are illustrated undamped and damped in different ways.

Figures 10a, 10b and 10c are drawings of preferred circuits for use with a resistive load in a negative pulse ampliiier, with a reactive load in a negative pulse amplifier, and for the cathode triggering of a positive pulse ampliiier with a resistive load, respectively.

Figures lla, 1lb, llc, 11d and 11e are various pulse inverter circuits for different circuit conditions.

Figure l2 is a graph showing the effect of a deionizing vapor included ina diode glow tube on the deionization characteristics.

Figure 13 is a graph of the electrical characteristics of a diode glow tube including a small amount of deionizing vapor.

Referring to Figure l the diode glow tube 1 consists pulse of a small glass envelope 2 containing two cold electrodes 3 and 4, and is lled with an inert gas to a pressure sutlicient to produce satisfactory glow discharge characteristics.

The envelope 2 can be made, for example, from suitable Kovar-sealing glass tubing and the electrodes 3 and 4 of short `parallellengths of Kovar wire, hydrogenannealed for obtaining a leak-proof seal, which are supported by aV press seal 5 of the glass tubing through which the electrodes extend and external leads can be connected. The envelope 2 can be made just large enough to contain the two electrodes 3 and 4 although larger envelopes will somewhat increase the operationallife of the tube. The diameter, Vlength and end shape of the electrodes arernot critical, and electrode spacing is chosen to give the desired electrical characteristics. -Either of the two electrodes can be used as the anode yand the other'as the cathode.

A preferred tube is approximately 0.25 inch in diameter,

1 inch long and each electrode can be made of Kovar wire 0.015 inch in diameter, 0.1 inch in electrode length, and spaced 0.10 inchY apart. An inert gas such as neon, for example, can'be used to till the tube to 200 mm. Hg of pressure'to obtain a desired tiring to burning voltage differential. g A

' In a diode glow tube filled with an inert gas as before described, for example, the voltage-current characteristics of an electrical dischargebetween electrodes can be obtained with the circuit of Figure 2. The diode l, there shown, is placed inseries with a variable Vresistance Ry and a milliammeter MA. A voltmeter V is connected 3; consist of a tiring potential A and a burning potential versus current curve D. Forglow discharge currents above l ma. the burning potentialrisesgradually with the increase of current. In the range from 0.1 ma. to 1 ma., the voltage-current curve D is nearly flat although a negative slopeeis displayed at'theI lowA current-end offthe curve, The glow is generally unstable for currents below about 0.1 ma; Y

The potential of ring, point A, will depend upon the degree of initial ionization present in the gays. Figure 4 illustrates graphically the deionization characteristics, curve E, of the diodeV glow tube 1. The tiring to burning voltage differential {A--D), whichlisl the voltage ditference between the tiring potential A and the burning voltage D, is plotted as a function, onf deionizationtime, that is, the time betweenkv quenching of glow .dischagge and retiring. It theV time delay is` short, as range.V a, Figure 4, then the residual ionizationremaining isvhigh and the tiring potential is correspondingly lower, However, if the deionization time is long, as in range c, then the existing low residual ionization permits the ringpotential to be erratic in a wide range above the more stable, short dcionization time tiring potential.y Thercis, however, an intermediate optimum range'b wherethe tiring potential is stable and independent of deionization time.

if the ionization lcvel is low, then the firing potential can easily be affected by cosmic rays, photo-electricemission, static charges on the envelope and other factors which tend to produce undesired'liuctuations oE-iiring potential. In the present-method astableiiring potential is obtained by the employment ofk residual ionization remaining momentarily after a state. of` conduction; that is, the tube is normally conducting ,and the glow discharge is quenched only for suicient time within the/optimum range b to allowenergy storage for an output pulse. Operation in the optimum range b results in output pulses of consistent amplitude regardless of input pulse amplitude or duration. The quenching isperformed by applying a suitable quenching pulse from a pulse source P providing pulses tending todecrease the conducting tube potential, and can be applied via .an input capacitor C as shown in the circuit of Figure 5. B-lvoltage, there shown, is supplied through a current limiting resistance R to the diode glow tubey l so that the diode 1 is normally conducting.

Thus, a negative input pulse 'appliedA to the diode 1 through the input-capacitor C (see Figure 5) can extinguish the tube current momentarily. Figure 6 shows plotted a tiring potential curveF for time after triggering. Also shown therein is the response of .tube potential toV a quenching input pulse. The broken curve in-Figure 6 indicates the tube response to theV quenching. There is a drop M in tube potential in response to the-input pulse reducing 'tube potential thereby causing extinction of glow discharge current. The anode would, therefore, rise in potential toward the B+ supply and retiringY will later occur. at a point X on the tiring potentialrcurve which depends upon the width of the input pulse and the rate or" R-C rise N 4of potential across the now nonconducting tube. A sharp-drop in tube potential Vto the burning potential takes place on tiring at the point X. A minimum deionizing time delaynmust be allowedreither by sutlicient input pulse width or R-C time constant, slowing the rate of tube potential rise in order to enable the tiring potential to reach the optimum range plateau for firing corresponding with range b in Figureftt.. The drop in tube potential upon tiring is very rapid and can permit the stored energy discharge of a high current surge from a parallel connected capacitance to an output load. The time interval from quenching to subsequent retiring can be used-asa pulse delay.

The diode pulse amplier is illustrated-in block diagram form in Figure 7 and consists Vof a pulse sourcev and input circuit section I, the diode glow tube andlvoltage supply section II, and-an output circuit and loadsection III. o Sectiong'l inpludes` ai pulse ,source .which providesthrough suitable impedance in the input circuit, the trigger pulses for quenching the subminiature gas discharge diode which is held normally conducting by a high voltage supply applied to the anode through a tube current limiting resistor in section II. The output circuit impedance of section III includes the output capacitor for energy storage following-quenching to provide a high current pulse to an output load.

Itcan be noted from the electrical characteristics illustrated for the subminiature diode glow tube before described, at the low current end of the burning voltage characteristic of Figure 3, for example, the negative slope of the curve at this section indicates that the tube 1 will oscillate in this current range if a parallel capacitor C1 is connected across it as-shown in- Figure 8a. The diode 1 is supplied with B+ voltage through a current limiting resistance R. The oscillation can be of a low amplitude asthe current shifts between-two,pointsV on the negative slope of the conductorvcurve, or it can be of high amplitude if the circuit time constants are long enough to permit quenching and, subsequent. retiring. Oscillation can be prevented by addinga damping resistor R1 in series with the capacitor C1 as shownin Figure 8b, or by adding-a dampingresistor R2 .and-series capacitor Ca connected across .thediode las .in Figure 8c.

Figure 9a illustrates Va diode glow tube l, B+ power supply circuit including the limiting resistor l and an undamped input circuit wherein a negative pulse source -P is connected tothe input capacitor C. lf the pulse source of the input circuit section is of low resistance, it can cause Ioscillation whencoupled to the tube 1 as shown. vThe addition of a series damping resistor Ra as in Figure 9b can provide damping and prevent oscillation, but willtalso attenuate the input pulse. To obtain damping Without input pulseiattenuation, a crystal diode Xi can be inserted in series with the input capacitor C Ias shown in Figure 9c, Ioriented to pass fthe negative input pulse and allow full utilization of Ithe input capacitor C in obtaining sufficient R-C ydeionization time, yet will bloclcwhen the tube-1 retires. Any small `oscillationof the tube potential immediately sets up a self bias across the crystal Xi placing it in 'a resistive state where it e'ifectively damps further oscillation. The crystal diode X1 so used also tends to block the lcoupling of output pulses back into the ,pulse source.

If the pulse source, is of exceptionally high resistance, then it will not permit the input capacitance C to act effectively in IObtaining time delay. In this case, arparallel crystal diode. can be conncctedyacross the pulse source as shown in ,Figure ,9d, or a series crystal diode Xs and capacitor C3 combination canbe connected across the tube 1, is in Figure` 9e, to obtain the. desired operation.v Crystals which areV therein shown soA placed offer Vhigh resistanceto input pulses, hence do no seriously attenuate them but provide la low resistance ,pa-th for -time delay charging of the capacitors C and C3.y

High sensitivity to Vtriggering can be obtained with crystal diode damping.- The tube is placed onpthe verge of oscillation -by suitable vcapacitance loading,- then a very small input pulse ywill nudge it into a quench oscillation. When the anode lreaches the "ring potential'following extinction, the tube will retire and the voltage consequently developed across the crystal diode exponentially decays to zero providing momentarily Asuiicient damping-'action to prevent continued-oscillation. Y

The same capacitors which furnish R-CA time Vdelay also can provide youtput pulse energy upon retiring. The available .pulseA energy is dividedA among' the input circuit, ,the B+ supply circuit, the dynamic resistancev of the tube and the output-circuit. The input circuit impedance can usually be made suiciently high that itand the necessarily high supplyV current` limiting resistor R subtract-but littlet'ronrthe-pulseenergy.Y In order for the load to receive a majority of the available energy, the-output-couplingeapacitormust form a majority of .5 the R-C time delay, and the load resistance must be greater than the dynamic resistance of the tube.

For high sensitivity to triggering from a high impedance input, it is necessary that `a relatively low impedance output load does not shunt out and thus greatly attenuate the input pulse. This can be accomplished by the insertion into the output circuit of a non-linear device such as a germanium crystal diode which -oters a high resistance to the low amplitude triggering pulse, but as the back voltage is increased such as by the higher potential retiring pulses, the dynamic resistance approaches zero and permits a high current pulse to pass. The crystal X4 in Figure 10a, so placed before the output load LR, does not interfere with the charging of output capacitor Co, and it also, in combination with the relatively low load resistance of LR, provides eective oscillation ydamping for the circuit.

The diode pulse amplilier is equally sensitive to triggering by pulses generated in the output load as it is to pulses in the input circuit. Precaution hence must be taken to prevent passage back to the amplifier of pulses generated by inductive load kickback or by the firing of some gas tube in the load. Any type of rectifying device may be used for this purpose. The circuit of Figure b has two crystal diodes, X5 performing the same function as crystal diode X, in the circuit of Figure 10a and Xe for blocking negative pulses generated by load LL. Reliected negative pulses are dissipated by shunt resistor R4 4and may be further attenuated 'by a parallel capacitor C4.

All the above circuits have indicated triggering by negative pulses applied to the anode electrode. The tube is equally responsive to positive pulses applied to the cathode. For example, to convert the circuit of Figure 10a to cathode triggering, it is only necessary to change B+ 4to B-, and reverse the crystal diode X4; then positive output pulses will be obtained from positive input pulses in the circuit of Figure 10c.

In addition to pulse amplification, the diode gas tube may also be used for pulse inversion. Figure 11a shows a circuit for converting negative input pulses to positive output pulses and Figure 11b a circuit for converting positive input pulses to negative output pulses. It is noted the input and output connections are on opposite sides of the tube 1 and the output to the load L is essentially in series with the input. Circuit simplicity is obtained in that the input capacitor C can also serve as the energy storage and output capacitor. Crystal diode X1 damping is indicated, the crystal diode X1 being reversed with a positive pulse source +P in Figure 1lb. The circuits of Figures 11a and 11b are for use with low impedance inputs. A high impedance input should utilize the circuits of Figure llc wherein the input is shunted by a crystal diode X2, and Figure 11d wherein the series combination of a crystal diode X3 and capacitor C3 is connected across the tube 1 and load L. The circuits of Figures lla, 1lb, llc and 11d indicate a low impedance load. If the load L has a high impedance, it can be shunted by a resistor, such as R3 in IFigure 11e.

A tube having the deionization characteristics of Figure 4 can operate at a maximum pulse rate of about 1000 pulses per second. The speed of operation is limited by the deionization time necessary to reach a consistent tiring potential. If high energy output pulses are desired, then the speed may be further restricted by the time necessary to charge a large output capacitor. Increasing the steady state tube current to obtain higher charging rates is limited by the insensitivity of the tube to triggering at high currents.

The characteristics shown in Figure 3 and 4 are considerably altered by the presence of a small percentage of polyatomic gas or vapor impurity mixed with the inert gas. In general, the impurity will raise the stable fu'- ing and burning potentials, and may extend the depth of the erratic firing potential range to several hundred volts.

As indicated by Figure 12, curve G, the deionization time required to reach the stable iiring potential` plateau is al most negligible in contrast to that without vapor (broken curve). In practical applications, the minimum time delay between triggering and retiring is limited by the rela` tively long time constants of even the smallest input and output capacitors that can be used.

The electricaltube characteristics of Figure 13 s'howing the burning potential-current curve H with deionizing vapor added, such as for example 1% water vapor, to the inert gas in a diode glow tube is similar to the curve er Figure 3, without vapor, .except that the vapor causes a higher minimum current breakof point below which stable conduction cannot exist. In this unstable range the rate of deionization is apparently greater than the rate of ion production by electron bombardment.

If the steady state tube current is set in the stable range just above the breakoi point by choosing the cur rent limiting resistor R of proper value, then a small trigger pulse, for example, 20 volts in magnitude with rise times of l microsecond or less, momentarily reducing the current below breakoif will quench the discharge. The tube will relire when the potential across it has risen to the firing point. The heavier vapor molecules cause rapid quenching of the discharge when the voltage gradient is momentarily lowered by the input pulse. The dissociated quenching gas or vapor automatically combines, giving the tube a reasonably long life. Sensitivity to triggering can thus be obtained at relatively high tube currents. The unstable current region below breakotf can be extended and triggering sensitivity can be increased still further by suitable capacitance loading across the tube. Consequently, much higher pulse repetition rates can be handled. With tubes of the present construction, upper limits of the pulse repetition rate is of the order of kc. per second, and minimum time delay of approximately 5 microseconds.

While in order to comply with the statute, the `invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect and the invention is, therefore, claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

l. A diode pulse amplifier comprising a gas-filled glow tube at glow discharge pressure and containing two symmetrical cold electrodes, one of said electrodes to act as an anode and the other as a cathode,a high D. C. voltage supply for said glow tube, a current limiting resistance connecting said anode to one terminal of said supply, said cathode connecting with the other terminal of said supply to maintain said glow tube in a normally conducting condition, a pulse source, coupling means connecting said pulse source across said electrodes, said pulse source being of a predetermined polarity to provide quenching pulses tending to decrease the conducting potential of said glow tube and place it momentarily in a non-conducting condition; and an output circuit connected across said electrodes and comprising a series combination of a capacitive energy storage means, a crystal diode, and a low resistance load, said capacitive energy storage means and said crystal diode reducing the shunting effect of said low resistance load.

2. A diode pulse amplifier comprising a gas-tilled glow tube at glow discharge pressure and containing two symmetrical cold electrodes, one of said electrodes to act as an anode and the other as a cathode, a high D. C. voltage supply for said glow tube, a current limiting resistance connecting said anode to one terminal of said supply, said cathode connecting with the other terminal 0f said supply to maintain said glow tube in a normally conducting condition, a pulse source, coupling means connecting said? pulse source; across said* electrodes, said pulse source being Iof-a predeterrniluzdl polarity toprovi'de quenching pulsestending to decrease the conducting potential of saidglow-tube and place it momentarily in a non-conducting condition; and an output circuit connected across said electrodes and comprising a series combination or a capacitive energy storage means, a rstand a second crystal diode disposed in opposing orientation, and a reactive load, with Va parallel combination of a dissipative resistance Aand capacitance connected across the series combination of said second crystal diode and said reactive load, to attenuate reflected pulses from said reactive load.

3. A diode pulse inverter comprising a gas-filled glow tube at glow discharge pressure and containing a rst and a second cold electrode, a high D. C. voltagesupply for said glow tube, a current limiting resistance connecting one terminal of-said voltage supply to said rst electrode, -alow internal impedance pulse source, said source bengof a predetermined polarity to provide input quenching-pulses to said glow tube, a series combination of an oscillation damping crystal diode and energy storage capacitance connecting said pulse source between said first electrode and the other terminal of said voltage supply, and a load connected between said second electrode and said other supply terminal.

4; A diode pulse inverter comprising a gas-filled glow tube at glow discharge pressure and containing a first and a second cold electrode, a high D. C. voltage supply, a current limiting resistance connecting one terminal of said voltage supply to said iirst electrode, a high internal resistance pulse source, said pulse source being of a predetermined polarity to provide input quenching pulses to said glowtube, a series coupling and energy storage capacitance connecting said pulse source between said rst electrode and the other terminal of said voltage supply, la shunting crystal diode connected across said pulse source,` and a load connected between said second electrode and said other supply terminal.

5. ,A diode pulse invertercomprisinga gas-iilled glow tube at glowdischargepressure and containing a first and aisecond coldelectrode, a' high D. C. voltage supply, a resistance connecting one termin-al of said voltage supply-to saidflrst electrode, ahigh internal resistance pulse source, `said pulse source being of apredetermined polarity to provide input quenching pulses to said glow tube, a series coupling capacitance connecting said pulse source between said first electrode and the other terminal of said voltage supply, aload connected between said second electrode and said other supply terminal, and a series combination of a second capacitance and a crystal diode connected across the series combination of said glow tube and load.

6. A diode pulse inverter comprising 1a gas-filled glow tube .at glow discharge pressure-and containing a first and a second cold electrode, a high D. C. voltage supply, a iirst resistance connecting one terminal of said supply to said iirstelectrode, a high internal resistance pulse source, said pulse source being of a ypredetermined polarity to provide input quenching pulsesl to said glow tube, a series coupling capacitance connecting said pulse source between said trst electrode and the other terminal of said supply, a high impedance load connected between said second electrode and said other supply terminal, and a second resist-ancev connected across said load to reduce elective output load impedance.

References Cited in the le of this patent UNITED STATES PATENTS 1,680,377 Holden Aug. 14, 1928 2,021,034 Thompson Nov. 12, 1935 2,088,495 Swedlund July 27, 1937 2,235,667 Blount et al Mar. 18, 1941 2,457,125 Chatterjea Dec. 28, 1948 V2,495,768 Reeves Ian. 31, 1950` 

